Impulsing circuit



y 1947- H..J. MCCREARY ,713

IMPULSING CIRCUIT Filed Nov. 23, 1944 BUSY TONE DIAL TONE IN V EN TIR.HAROLD J. M

ATTORNEY v ratio is the optimum ing conditions and allows considerabletolerance switching mechanism under Patented May 20, 1947 IMPULSINGCIRCUIT Harold J. McOreary, Lombard, 111.,

Automatic Electric La 111., a corporation of assignor to boratories,Inc., Chicago, Delaware Application November 23, 1944, Serial No.564,880

10 Claims. 1

The present invention relates to impulsing circuits such as are used tocontrol the operation of stepping switches in automatic telephonesystems, and is more particularly concerned with arrangements forimproving the reliability of operations of such switches when thecontrol impulses are transmitted over lines of poor characteristics.

The usual impulsin devices which are located at the subscribers stationsof an automatic telephone system are constructed and adjusted to providea fixed ratio between the break period and the make period of theimpulses which they produce. The ratio commonly used in'telephonesystems of the StroWger type provides a break period equal to fil of theimpulse period. This value for average operatin the impulse speed, lineresistance, line leakage, exchange voltage, and adjustment of theswitching mechanism in the exchange. Variations of any of thesequantities from their nominal values produce variations in the length ofthe impulse delivered to the switch magnets by the line relay in theexchange switching equipment. However, cases often arise Where it isdesirable to increase the permissible tolerance limits'in order toprovide increased reliability of operation of the unusually poorimpulsing conditions.

The principal object f the present invention is to provide a new andimproved impulsing circuit which will deliver impulses having a fixedclosure time in response to received impulses of .variable speed andimpulse ratio.

.A,further object of the invention is to provide an impulsing circuit inaccordance with the preceding object in which the fixed closure time ismeasured by means of a resistor-condenser combination and a thermionictube.

Another object is to provide a telephone selector switch employing meansfor delivering pulses of a fixed duration to the switch magnets andincluding circuit arrangements for delivering pulses of greater lengthto the changeover relay which -must remain operated during a series ofreceived impulses.

A feature of the invention is the provision, in a selector switch havingmeans for providing a fixed length of pulse to the magnets, of means forpreenergizing the line relay to increase the length of ithe impulsesdelivered to the holding relay.

Other objects and features of the invention will appear upon afurtherperusal of the specificaqtion taken in connection with the accompanyingdrawing which illustrates in the form of a schematic diagram theapplication of the invention to a two-motion telephone selector switchof the Strowger type.

Briefly described, the invention consists .in providin a timin circuitcomprising a, thermionic tube'having a delay network consisting of acondenser and a resistor in its grid circuit, and a pair ofrelaysarranged tobe-controlled by contacts of the usual line relay andby the thermionic tube so as to initiate the operation of the timingmeans in response to each restoration of the line relay and to repeatpulses of a fixed duration, determined by the time constant of the delaynetwork in the .grid circuit of the thermionic tube, to the switchmagnets. Circuit arrangements'ineluding contacts of the preceding pairof relays are providedto insure that a circuit is closed to thechangeover relaywhile the line relay is restored or while a circuit isclosed to the switch magnets. Referring now to the drawing, relay A isthe usual line relay, relay B is the usual holding relay, relay C is theusual changeover relay, relay D is normally a slave relay to relay B,relay is the usual rotary stopping relay, relay F is a, slave relay tothe usual vertical off-normal springs, relay H. is the usual switchingthrough relay, magnets V, R0, and RL are the usual vertical, rotary, andrelease magnets, relays G and J are additional relays associated Withthe improved impulsing circuit, and thermionic tube [0 togetherwith thedelay networkconnected in its grid circuitconstitutes the timing meanswhich determines the duration of the pulses delivered to the verticalmagnet V.

In. order that the inventionmay bestbe understood, a detaileddescription of the operation of the selector switch incorporating theinvention will be given. Forthis purpose it will be assumed that theselector switch is seized in the usual manner over leads I, 2 and 3, bya preceding line finderorrotary lineswitch. When the selector is seizeda loopcircuit is closed to line relay A over leads l and ii, and acircuit is closed to theupper winding of changeover relayC over leads.Relay A operates and closes a multiple circuit to relays B and G. RelayG operates and prepares. a circuit to relay J. Relay (3' operates. 4

Relay l3 operates, grounds lead 3 to hold the preceding switch and relay0, closes a circuit to relay D through the cam springs CS, and furtherpreparesthe circuit to relay J Relay D operates,

further prepares the circuit to relay J, and prepares circuits for therotary magnet R and the rotary stopping relay E.

When the calling subscriber dials the first digit of a desired numberrelay A is momentarily restored a number of times corresponding to thedigit dialled. Each time that relay A restores it completes a circuit tothe upper winding of relay J and opens the circuit to relays B and G.Relay B is made slow to release by a copper sleeve on its core so thatit will remain operated during impulsing. Relay J operates, closes itslocking circuit through its preliminary make contacts J l, disconnectsrelay G from relay B to prevent the shunting effect of relay B fromretarding the release of relay G, completes a multiple circuit to thevertical magnets V and the lower winding of relay C, and disconnectsnegative battery from the grid of thermionic tube i5. Relay G restores,opens the operating circuit to relay J, and prepares a second circuitfor the uppe' winding of relay C. The vertical magnets V operate toraise the switch shaft to the first level of bank contacts, and operatethe vertical magnet springs VI to close a circuit through resistor M torelay A. Resistor M has a value sufficiently high so that relay A willnot operate in series with it, but the operate time of relay A isappreciably reduced due to this pie-energizing circuit thus permittingit to operate more quickly when the loop circuit over leads I and 2 isreclosed. The effect of the pre-energization of relay A is to increasethe duration or the impulses delivered to relay 13 during diallinginsuring its continued operation.

The filament of tube 1% is energized from the exchange battery in serieswith resistor ll. The cathode of the tube is connected to the junctionbetween resistor ii and the filament so that it is maintained at anegative potential with respect to ground by an amount equal to thevoltage drop across the resistor H. The anode of tube i9 is normallyconnected to the negative terminal of the exchange battery through thetwo windings of relay J in series thus maintaining the anode negativewith respect to the cathode. However, when ground is connected to theupper winding of relay J by relay A the anode of tube i3 is madepositive with respect to the cathode. Tube 10 does not conduct currentat this time due to the negative bias placed on its control grid bycondenser l2, which is normally charged to a potential equal to thevoltage drop across the filament of tube it. The operation of relay Jopens this charging circuit and thus permits condenser E2 to dischargethrough resistor 3. The values of condenser i2 and resistor 13 arechosen so that the grid bias on tube 19 will reach a point where thetube is rendered conducting in a time equal to the desired length ofpulse to the vertical magnets V. Resistor i3 is preferably madeadjustable to permit variation in the duration of the repeated impulsesas desired. To provide the most accurate timing tube 48 is preferably ofthe gas discharge type so that the anode current of the tube willincrease abruptly from zero to a finite value when its grid reaches acritical potential rather than increasing gradually as it would do iftube 18 were of the high vacuum type. In the following description itwill be assumed that the gas discharge type of tube is used. When tube19 fires it causes the lower winding of relay J to be energized inopposition to the upper windin Relay J consequently re stores, opens thelocking circuit to its upper winding and removes ground or plus batteryfrom the anode of tube Ii) at contacts J 1 thus causing the tube tobecome deionized, opens the circuit to the vertical magnets V,reconnects relay G in multiple with relay B so that it will bereoperated after A reoperates, and recloses the charging circuit tocondenser 22. When relay A reoperates it recloses the multiple circuitto relays l3 and G. Relay G again operates and prepares the circuit tooperate relay J by its upper winding the next time that relay Arestores. The switch is now in the same condition as when first seizedexcept that the vertical magnets have raised the switch shaft onevertical step thus bringing about the operation of the vertical offnormal springs VON. These springs complete a circuit to relay I? whichoperates, transfers the upper winding of relay C from ground on lead 3to contacts of relay G, disconnects dial tone from the calling line, andprepares circuits to the rotary magnets R0 and the release magnet RL.During succeeding impulses oi the first digit relay J is operated andrelay G released in response to the restoration of relay A. When relay Grestores it closes a circuit to the upper winding of relay C from backcontacts oi relay A. The object of this last circuit is to provide alonger length of impulse to relay C than it receives from its lowerwinding alone. The succeeding impulses are repeated to the verticalmagnets V by relay J in the same manner as the first impulse.

.At the conclusion of the series of impulses relays A, B C, L, and G-will be operatcd and the switch shaft will have been raised to thedesired level. Relay C restores a short time after the last impulse andcloses a circuit to the rotary magnets R0 through the rotary interruptersprings B04. The rotary magnets operate selfinterrupted to advance theswitch wipers 4 to 6 over bani; contacts of the selected level. When thewipers reach an idle second selector or connector negative battery isextended to relay E over wiper from the succeeding switch. Relay Eoperates, opens the driving circuit to the rotary magnets R0 to stopiurther rotary liotion, and closes a circuit to relay E. Relay Hoperates, closes its locking circuit to lead 3, transfers the callingsubscribers loop from relay A to the succeeding switch over wipers 4 and5, extends the holding lead 3 to the succeeding switch over wiper opensthe impulsing circuit thus opening the circuits to relays and G, andopens a further point in the rotary magnet driving circuit. Relays A,and E restore. Relay B restores, opens the circuit to relay D, andremoves ground from the holding lead 3. During the release time of relayB the succeeding switch places a multiple ground on the holding leadover wiper which ground is under the control oi the calling subscribersloop circuit. Relay D restores. opens fur her points in the impulsingcircuit and rotary magnet driving circuits, and removes the operatingground from relay E. Relays H and F remain operated throughout theconnection. When the calling subscribers loop circuit is opened at theconclusion oithe conversation the succeeding switches remove the groundfrom the holding lead which is extended over wiper thereby opening thecircuit to relay H. Relay H restores and closes a circuit to the releasemagnet which operates to permit the switch shaft to return to normal.When the shaft is restored the vertical off normal springs open andrelease relay P which restores and opens the circuit to the releasemagnet RL.

In the event that there were no idle second selectors or connectorsavailable on the selected level the rotary magnets would have driven thewipers beyond the last contacts in the level to the 11th rotary stepwhere cam springs CS operate and open the circuit to relay D. Relay Drestores, connects the busy tone lead in the calling line throughcondenser 7, opens incomplete circuits to relays E and J, and opens therotary magnet driving circuit to stop further operation of the magnetsR0. The calling subscriber hangs up upon hearing the busy tone thusopening the loop to relay A. Relay A restores and opens the circuit torelay B. Relay B restores, opens a further point in the circuit to relayD, closes a circuit to the release magnet RL, and removes ground fromlead 3 to release the preceding switch. The release magnet RL operatesto permit the switch shaft to restore to normal. Relay F is releasedwhen the vertical off normal springs open as previously described.

What is claimed is:

1. In an automatic switch having a line relay, a holding relaycontrolled by contacts of said line relay, and stepping means fordirecting the operation of the switch; timing means controlled bycontacts of said line relay operative to repeat impulses having a fixeddesired duration to said stepping means in response to the receipt ofimpulses of an undesired duration by said line relay, and meanscontrolled by said stepping means for pro-energizing said line relay tothereby increase a the average current in said impulsing.

2. In combination, a gas discharge tube having a cathode, an anode, anda control grid, a relay having two windings one of which is included inthe anode circuit of said tube, an operating circuit for said relayincluding its other Winding, contacts on said relay for causing anaperiodic voltage to appear between the control grid and cathode of saidtube in response to the operation of the relay, and said tube firingwhen said aperiodic voltage reaches a predetermined value to energizesaid one winding in opposition to said other winding and thereby causesaid relay to restore.

3. In a combination as claimed in claim 2, circuit arrangements causingsaid tube to be deionized in response to the restoration of said relay.

i. In combination, a thermionic tube having a cathode, an anode, and acontrol grid, a relay having two windings one of which is included inthe anode circuit of said tube, an operating circuit for said relayincluding its other winding, contacts on said relay for causing anaperiodic voltage to appear between the control grid and cathode of saidtube in response to the operation of the relay, and said tube becomingconductive when said aperiodic voltage reaches a predetermined value toenergize said one winding in opposition to said other winding andthereby cause said relay to restore.

5. In a signaling system, a first circuit over which impulses are attimes transmitted, a thermionic tube having a cathode, an anode, and acontrol grid, means associated with said first circuit for initiating animpulse over a further circuit and for initiating the flow of anaperiodic current in the grid circuit of said tube in response to thereceipt of an impulse over said first circuit, said aperiodic currentrendering the tube conductive a predetermined time interval thereafter,and said means being operated by the holding relay during anode currentof said tube to terminate the impulse over said further circuit.

6. In an automatic switch, a line relay, an auxiliary relay controlledby said line relay, timing means comprising a space discharge device, anaperiodic circuit, and a relay, a stepping magnet controlled by saidtiming means, circuit arrangements including contacts of said auxiliaryrelay for delivering a momentary impulse to said timing means inresponse to each restoration of said line relay, said timing means beinoperative to deliver an impulse of fixed duration to said steppingmagnet in response to said momentary impulse.

7. In an automatic switch, a line relay, an auxiliary relay controlledby said line relay, timing means, a stepping magnet controlled by saidtiming means, circuit arrangements includng contacts of said auxiliaryrelay for delivering a momentary impulse to said timing means inresponse to each restoration of said line relay, said timing means beingoperative to deliver an impulse of fixed duration to said steppin magnetin response to said momentary impulse, a changeover relay having twowindings, and circuit arrange-v ments for energizin one of said windingsby said timing means for the duration of said impulse and for at timesenergizing the other of said windings through contacts of said linerelay during its restored period.

8. In combination, a gas discharge tube having a cathode, an anode, anda control grid, a relay having two windings one of which is included inthe anode circuit of said tube, an operating circuit for said relayincludin its other winding, means for momentarily completing saidoperating circuit, contacts on said relay for completing a lockingcircuit through said other winding in response to the operation of therelay and further contacts on said relay for causing an aperiodicvoltage to appear between the control grid and cathode of said tube, andsaid tube firing when said aperiodic voltage reaches a, predeterminedvalue to energize said one winding in opposition to said other windingand thereby cause said relay to restore.

9. In combination, a thermionic tube having a cathode, an anode, and acontrol grid, a relay having two windings one of which is included inthe anode circuit of said tube, an operating circuit for said relayincluding its other winding, means for momentarily completing saidoperating circuit, contacts on said relay for. completin a lookingcircuit through said other winding in response to the operation of therelay and further contacts on said relay fo causing an aperiodic voltageto appear between the control grid and cathode of said tube, and saidtube becoming conductive when said aperiodic voltage reaches apredetermined value to energize said one winding in opposition to saidother winding and thereby cause said relay to restore.

10. In combination, a gas discharge tube having a cathode, a controlgrid, and an anode, an aperiodic circuit between the cathode and theanode of said tube, a relay havin two windings one of which is includedin the anode circuit of said tube, an operating circuit for said relayincluding its other winding, means for momentarily completing saidoperating circuit, contacts on said relay for completing a lockingcircuit through said other winding in the response to the operation ofsaid relay and other contacts on said relay for causing an aperiodicvoltage between the grid and the cathode of said tube, said aperiodicvoltage reaching a value to fire said tube in a predetermined time, theanode current of said tube energizing said one winding in opposition tosaid other winding and thereby cause said relay to restore, and means toadjust said aperiodic circuit for at times changing said predeterminedtime.

HAROLD J. MCCREARY.

REFERENCES CITED The following references are of record in the file ofthis patent:

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